Increasingly for the handling of stackable materials, e.g. paper, cardboard, paperboard and other sheet materials, the sheet materials are bundled to form a stack and the stack can be provided on a pallet. The stack may originally be strapped to the pallet or can be wrapped to hold the stack together and the palletized stack, i.e. the pallet with the stack thereon, can readily be shifted by a forklift truck or other forklift type of device, e.g. a fork-hoist, capable of lifting the pallet, moving the pallet with the stack thereon along the ground or floor, lowering the pallet and even placing one palletized stack above another. The palletizing of such stacks thus has been found to greatly enhance the ease with which the stack can be moved about, positioned and ultimately delivered to a machine or line in which the individual articles may be utilized.
At this point, the palletized stack must be broken down, i.e. the articles removed from the stack or, as stated otherwise, the pallet stacked with stackable elements, especially paper, must be destacked.
A conventional system for this purpose comprises a feed conveyor for advancing the pallet stacked with the stackable elements, e.g. paper, hereinafter referred to as a stacked pallet, to a destacking station, a destacking station to which the stacked pallets are supplied by the conveyor with a predetermined destacking level and a destacking table which can receive the stacked pallets in succession and is capable of raising and lowering so that the uppermost element of the stack may be brought to the destacking level, and a discharge conveyor for carrying off the destacked pallet, i.e. an empty pallet from which all of the elements of the stack have been removed.
The destacking level can, for example, be the feed level of a machine to be charged with the individual elements of the stack, e.g. a packaging machine, printing machine or package-making machine are fed with the individual elements as they are removed from the stack at this level. The removal of the elements at this level can be effected automatically with corresponding means, e.g. suction grippers, or by hand in the conventional apparatus and this type, only the destacking table is provided at the destacking station and it is moved between its lowest table level and a highest table level alternately based upon the height of the stack and directly receives the stacked pallet from the feed conveyor and directly transfers the destacked or empty pallet to the discharge conveyor.
The feed conveyor and discharge conveyor can be located at the same level and this latter level, at which transfer of the stacked pallet to the table and transfer of the empty pallet to the discharge conveyor takes place, can be intermediate the highest and lowest levels of the table.
In general, at this intermediate level, an empty pallet is fed to the discharge conveyor simultaneously with the advance of a stacked pallet onto the table from the feed conveyor.
Significant time waste occurs in this system since, for this operation, the destacking table initially must be brought from its highest position at which the last element is removed, into the intermediate position at which a new stacked pallet is shifted onto the table and the empty pallet is transferred from the table to the discharge conveyor, and then the table with the stacked pallet thereon must be lowered into the lowest position or level so that the uppermost element of the stack is located at the destacking level.
The resulting time waste can interrupt feeding to the machine which is processing the individual elements and can result in higher costs of manufacture and significant production losses.